Manufacturing Technology I. Lecture 3. Fundamentals of Cutting

Transcription

1 Manufacturing Technology I Lecture 3 Fundamentals of Cutting Prof. Dr.-Ing. F. Klocke Structure of the lecture Examples: turning of steel The cutting part - Terms and symbols The cutting operation Loads of the cutting part Influences exerted by the geometry of a cutting part on its characteristics under load Too wear Types of tool wear and tool wear measurements Wear mechanisms of the cutting process Summary 1

2 Structure of the lecture Examples: turning of steel The cutting part - Terms and symbols The cutting operation Loads of the cutting part Wear Influences exerted by the geometry of a cutting part on its characteristics under load Types of tool wear and tool wear measurements Wear mechanisms of the cutting process Summary Example: turning of steel, roughing source: Widia 2

3 Example: turning of steel, finishing source: Widia Structure of the lecture Examples: turning of steel The cutting part - Terms and symbols The cutting operation Loads of the cutting part Influences exerted by the geometry of a cutting part on its characteristics under load Tool wear Types of tool wear and tool wear measurements Wear mechanisms of the cutting process Summary 3

4 Terms at a simple cutting part h chip thickness thickness of cut (prior( before to deformation chip removal) ) chip wedge h ch chip depth thickness of cut ((after chip deformation removal) ) α 0 clearance tool orthogonal angleclearance h ch β 0 γ 0 leading tool orthogonal edge angle wedge angle effective tool orthogonal cutting rake angle γ 0 β 0 direction of cut h α 0 transient surface workpiece face flank Cutting edges and surfaces on the cutting part of a turning tool direction of cut shaft shank major second face minor cutting edge direction of feed land minor of the first minor flank cutting edge flank minor second minor flank corner cutting edge corner, with corner radius main major cutting edge major face first chamfer face of the major cutting edge major flank first chamfer flank of the major cutting edge major main flank second flank source: ISO 3002/1 4

5 Tool-in-hand system assumed working plane P f assumed direction of feed motion assumed direction of primary motion tool back plane P p tool cutting edge normal plane P n tool orthogonal plane P o tool cutting edge plane P s assumed direction of feed motion tool plane reference of reference plane P r P r selected point on the cutting edge source: ISO 3002/1 tool reference plane P r base Tool-in-use system direction of primary motion resultant cutting direction resultant cutting direction direction of primary motion direction of feed motion Wirk-Rückebene P pe working plane P fe working cutting edge plane P se direction of feed motion working plane P fe working orthogonal plane P oe working cutting edge normal plane P ne = P n selected point on the cutting edge working reference plane P re working reference plane P re source: ISO 3002/1 plane containing base of tool 5

6 Engagement in longitudinal cylindrical turning primary motion thickness of cut cross-sectional area Angles at a selected point on the cutting edge direction of primary motion section C-D assumed working plane P f tool reference plane P r tool reference plane P r section A-B selected point on the cutting edge section E-F tool back plane P p section Z major cutting edge source: ISO 3002/1 tool reference plane P r tool cutting edge inclination 6

7 Structure of the lecture Examples: turning of steel The cutting part - Terms and symbols The cutting operation Loads of the cutting part Influences exerted by the geometry of a cutting part on its characteristics under load Tool wear Types of tool wear and tool wear measurements Wear mechanisms of the cutting process Summary Chip formation trace of the shear plane material cutting material cross-sectional area shear zone transient surface 7

8 Strain rates of different manufacturing processes Process: Superplastic Forming Deep Drawing Hot Rolling Cold Rolling Bar- and Tube-Drawing High Speed Forging Wire-Drawing Explosive Forming Split-Hopkinson-Bar-Test Cutting strain rate ϕ& / s 7 strain tensor: 2 ε x 2 ε = xy γ xy γ xy 2 ε y Calculation of the strain rate rate of deformation strain rate v ε& x x = x v y ε& y = y shearing strain rate v v x y γ& xy = + y x strain tensor: xch 2 ln ϕ = x xy Φ + ψ γ o 2 0 v ε& z z = z vy vz γ& yz = + z y The outcome of the time derivation is the strain rate! & ϕ y = 2 lnλh t Φ + ψ γ o 2 lnλ l = hch Φ + ψ γ o 2 ln h x ch ϕ& x = 2 ln t x0 vz vx γ& zx = + x z Φ + ψ γ o 2 lnλh γ = Φ + ψ xy γ o Φ + ψ v r ch h 2 ε x γ xy 2 ε = ij workpiece γ xy 2 ε y v r c workpiece source: Leopold ψ Φ x ε x = x hch ε y = = λh h u Φ + ψ γ o = arctan h ξ = 0 ch 0 tool x ch γ o F y x 0 F x h u x h ch x ch h ch tool u y 8

9 Types of chip formation continuous chip segmented chip shearing chip very equal metallographic structure local hard deformed metallographical structure local nearly no deformed metallographic structure local hard deformed metallographic structure local nearly no deformed metallographic structure fractional seperation of segments Which type of chip formation is existent, is generally affected by the friction on the face. Structure of the lecture Examples: turning of steel The cutting part - Terms and symbols The cutting operation Loads of the cutting part Influences exerted by the geometry of a cutting part on its characteristics under load Tool wear Types of tool wear and tool wear measurements Wear mechanisms of the cutting process Summary 9

10 Conditions of the cutting process compressive stress stress characteristics chip velocity shearing stress average compressive stress average shearing stress g Components of the total force primary motion direction of feed motion total force back force 10

11 Influence of parameters on the components of the total force blue brittleness adhesion back force F p depth of cut a p Graphical determination of the parameters F c1.1 and (1-m c ) F c / N/mm F c1.1 = 890 N/mm Cutting force F c width of cut b thickness of cut h/mm 11

12 Distribution of effective work during the cutting process 7000 Nm material work W width of cut b tool orthogonal clearance α o tool orthogonal rake γ o source: Vieregge Distribution of heat and temperature in workpiece, chip and tool chip L = α L HS T 6 1 = mm 400 K K = 9, 6 µ m material thickness of cut tool orthogonal rake 12

13 Force components and chip temperatures in turning temperature aluminium steel / titanium feed 0,25 mm 0,1 mm depth of cut 2 mm 1 mm 500 cutting speed cutting force F c N Structure of the lecture Examples: turning of steel The cutting part - Terms and symbols The cutting operation Loads of the cutting part Influences exerted by the geometry of a cutting part on its characteristics under load Tool wear Types of tool wear and tool wear measurements Wear mechanisms of the cutting process Summary 13

14 Influence exerted by cutting edge geometry on machining parameters low minimum thickness of cut : low r n to decreasing wear decreasing wear major first face decreasing wear reduced chatter vibrations lower cutting force to to increasing back force and cutting part stability better surface integrity reduced the probability of chatter vibrations controlled chip flow to Structure of the lecture Examples: turning of steel The cutting part - Terms and symbols The cutting operation Loads of the cutting part Influences exerted by the geometry of a cutting part on its characteristics under load Tool wear Types of tool wear and tool wear measurements Wear mechanisms Summary 14

15 Types of tool wear and tool wear measurements flank wear land KF c major flank wear land minor flank wear land KF tool orthogonal rake tool orthogonal clearance width of flank wear land crater front distance cutting edge offset in face direction cutting edge offset in flank direction Structure of the lecture Examples: turning of steel The cutting part - Terms and symbols The cutting operation Loads to which the cutting part is exposed Influences exerted by the geometry of a cutting part on its characteristics under load Tool wear Types of tool wear and tool wear measurements Wear mechanisms in cutting processes Summary 15

16 Wear mechanisms in cutting processes abrasion oxidation source: Vieregge Comb and transverse crack formation in milling operations width of flank wear land source: Lehwald, Vieregge 16

17 Plastic deformation of the cutting edge 20 µm work material tool material cutting speed cross-sectional area of cut cutting part geometry Ti Al 6V 4 HS vc = 8 m/min ap f=1,5 x 0,25 mm2 rε γ0 α0 λs χr εr 5o 8o -4o 75o 90o 0,5mm cutting time tc=1 min, cycles-to-failure N = Flank wear and formation of build-up cutting edge vc = 2 m/min vc = 20 m/min vc = 10 m/min 0,1 mm vc = 30 m/min vc = 40 m/min width of flank wear land HW-P30 formation of build-up cutting edges cutting part geometry ααo0 γγ0o λλs0 εε0r cutting time tc = 30 min κκr0 rrεε 60 1 mm 17

18 Flank wear at turning tools width of flank wear land VB 0,24 mm 0,20 0,16 0,12 0,08 f = 0,4 mm cutting part geometry γ 0 α 0 λ s χ r ε r r ε 8 o 10 o -4 o 90 o 60 o 1 mm cutting time t c = 30 min f = 0,25 mm f = 0,1 mm 0,04 material Ck53N cutting material HS depth of cut a p =2mm m/min 100 cutting speed v c Simplified representation of diffusion process in cemented carbide tools case hardened steel C10 quenched and tempered steel Ck53 chip C Fe C Co A B cemented carbide P30 tool cemented carbide P30 TiC - WC (TaC/NbC) Co WC - solid solution solution of WC to: Fe 3 W 3 C; (FeW) 6 C; (FeW) 23 C 6 Zone A: Fe-Co-MK Zone B: Co-Fe-MK 18

19 Oxidation zones of a cemented carbide turning tool oxidation face oxidation zones flank material cutting material cutting speed cross-sectional area cutting time Ck53N HC-P30 v c = 125 m/min a p f = 3 0,25 mm² t c = 20 min Structure of the lecture Examples: turning of steel The cutting part - Terms and symbols The cutting operation Loads of the cutting part Influences exerted by the geometry of a cutting part on its characteristics under load Tool wear Types of tool wear and tool wear measurements Wear mechanisms in cutting processes Summary 19

20 List of questions I Identify the different cutting edges and areas of a turning tool! Specify and explain the angles for determination of the orientation and shape of the cutting part! Specify the types of chip formation and explain their development! In which plane do you measure the tool angles? List the orthogonal components of the total force! Illustrate qualitatively the dependence of feed, cutting speed, cutting depth and tool cutting edge angle on the total force components! Explain the dependence! Specify an empirical force equation and explain the characteristic parameters! Where can you identify heat sources during chip formation and how dissipates the major heat? Please identify the place of the highest cutting temperature? List of questions II Specify the influencing factors for choosing the geometry of the cutting part! How to increase the stability of the cutting edge? Specify the influencing variables to reduce the probability for chatter vibrations! Identify and explain the types of tool wear at the cutting part! Signify the major tool wear measurements! Specify the wear mechanisms and indicate their dependence of the cutting speed. Explain comb and transverse crack formation! Illustrate the term built-up edge formation and explain the progression of the flank wear land and the surface roughness dependent on the cutting speed! 20